1. Field of the Invention
The present invention is generally in the field of electronic circuits and systems. More specifically, the present invention is in the field of class-D amplifier circuits, so called switching power amplifiers.
2. Background Art
Class-D amplifiers, also called switching amplifiers, provide power-efficient amplification, a property that is particularly important for applications in which a battery is used as a power source. Though potentially capable of producing a highly power-efficient amplified signal, conventional class-D amplifiers are often difficult to adapt for mobile audio applications such as cellular and mobile communications applications. Unfortunately, noisy environments in such applications significantly deteriorate the performance of conventional class-D amplifiers.
For example, conventional open-loop class-D amplifiers typically exhibit poor performance, such as a high THD+N ratio or low supply rejection ratio, which effectively prevents these amplifiers from being adopted in high fidelity audio drivers. Closed-loop class-D power amplifier configurations have been developed to address such issues. However, such configurations have been largely unsatisfactory in mobile applications, especially when driving a large signal. In a conventional closed-loop class-D amplifier, loop filter outputs swing with output signal amplitude. If the output signal amplitude is close to the supply voltage rail, a small fluctuation in the supply rail can make the loop filter output voltage hit the rail voltage and the loop can saturate very easily. When the loop saturates, the overall performance of the class-D amplifier degrades significantly and its power driving capability is also seriously diminished. Consequently, conventional closed-loop approaches to addressing the issues of open-loop class-D configurations may themselves undesirably limit the power driving capability of the switching amplifiers and negate one of the key implementational advantages of switching amplifier technology.
Accordingly, there is a need to overcome the drawbacks and deficiencies of the conventional art by providing a high performance closed-loop class-D amplifier circuit displaying enhanced supply rejection and performance, which is suitable for implementation as an audio amplifier in a mobile communications device.